Not going to work in this world.
Indeed, a wizard who develops too much of a specialization is going to find other problems arising. (Perhaps fire makes him angry, water weakly compliant, air flighty, earth lazy -- for a start.) In RPG terms, they do have opposed schools, but those that deal with non-material things like illusions and mind-affecting spells.
Harmony between the elements is a big thing in this world, partly because the imbalance is quite dangerous. There are specialist elementalists, there are cults of individual elements that tout one's virtues and downplay all those of the rest, there are sorcerers who can channel elemental powers, and every one of them is a danger and generally a villain.
And that's going into the way where I may have not the elemental planes but the elemental borders -- the world of humanoids lies in the point where they all meet, and are mixed and made harmonious. And the borders can be endlessly pushed back, but only with great effort and magic.